package agent

import (
	"context"
	"fmt"
	"time"

	"github.com/spf13/cobra"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	"k8s.io/apimachinery/pkg/labels"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/cli-runtime/pkg/genericclioptions"
	"k8s.io/klog/v2"

	monov1alpha1 "example.com/monok8s/pkg/apis/monok8s/v1alpha1"
	mkscmd "example.com/monok8s/pkg/cmd"
	osupgradeController "example.com/monok8s/pkg/controller/osupgrade"
	"example.com/monok8s/pkg/kube"
	"example.com/monok8s/pkg/templates"
)

const defaultPollInterval = 15 * time.Second

var runtimeDefaultUnstructuredConverter = runtime.DefaultUnstructuredConverter

func NewCmdAgent(flags *genericclioptions.ConfigFlags) *cobra.Command {
	var namespace string
	var envFile string
	var pollInterval time.Duration

	cmd := &cobra.Command{
		Use:   "agent --env-file path",
		Short: "Watch OSUpgrade resources and process matching upgrades for this node",
		RunE: func(cmd *cobra.Command, _ []string) error {
			if envFile == "" {
				return fmt.Errorf("--env-file is required")
			}

			if err := mkscmd.LoadEnvFile(envFile); err != nil {
				return fmt.Errorf("load env file %q: %w", envFile, err)
			}

			vals := templates.LoadTemplateValuesFromEnv()
			rendered := templates.DefaultMonoKSConfig(vals)
			cfg := &rendered

			if cfg.Spec.NodeName == "" {
				return fmt.Errorf("node name is empty in rendered config")
			}

			klog.InfoS("starting agent",
				"node", cfg.Spec.NodeName,
				"namespace", namespace,
				"envFile", envFile,
				"pollInterval", pollInterval,
			)

			clients, err := kube.NewClients(flags)
			if err != nil {
				return fmt.Errorf("create kube clients: %w", err)
			}

			ctx := cmd.Context()
			return runPollLoop(ctx, clients, namespace, cfg.Spec.NodeName, pollInterval)
		},
	}

	cmd.Flags().StringVar(&namespace, "namespace", "kube-system", "namespace to watch")
	cmd.Flags().StringVar(&envFile, "env-file", "", "path to env file containing MKS_* variables")
	cmd.Flags().DurationVar(&pollInterval, "poll-interval", defaultPollInterval, "poll interval for OSUpgrade resources")

	return cmd
}

func runPollLoop(ctx context.Context, clients *kube.Clients, namespace, nodeName string, interval time.Duration) error {
	gvr := schema.GroupVersionResource{
		Group:    monov1alpha1.Group,
		Version:  monov1alpha1.Version,
		Resource: "osupgrades",
	}

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		if err := pollOnce(ctx, clients, gvr, namespace, nodeName); err != nil {
			klog.ErrorS(err, "poll failed", "namespace", namespace, "node", nodeName)
		}

		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
		}
	}
}

func pollOnce(
	ctx context.Context,
	clients *kube.Clients,
	gvr schema.GroupVersionResource,
	namespace string,
	nodeName string,
) error {
	list, err := clients.Dynamic.Resource(gvr).Namespace(namespace).List(ctx, metav1.ListOptions{})
	if err != nil {
		return fmt.Errorf("list osupgrades: %w", err)
	}

	klog.InfoS("agent tick", "namespace", namespace, "items", len(list.Items), "node", nodeName)

	nodeLabels := labels.Set{
		"kubernetes.io/hostname":   nodeName,
		"monok8s.io/node-name":     nodeName,
		"monok8s.io/control-agent": "true",
	}

	for i := range list.Items {
		item := &list.Items[i]

		osu, err := decodeOSUpgrade(item)
		if err != nil {
			klog.ErrorS(err, "failed to decode osupgrade",
				"name", item.GetName(),
				"resourceVersion", item.GetResourceVersion(),
			)
			continue
		}

		if !matchesNode(osu, nodeName, nodeLabels) {
			klog.V(2).InfoS("skipping osupgrade; not targeted to this node",
				"name", osu.Name,
				"node", nodeName,
			)
			continue
		}

		klog.InfoS("matched osupgrade",
			"name", osu.Name,
			"node", nodeName,
			"desiredVersion", osu.Spec.DesiredVersion,
			"phase", statusPhase(osu.Status),
			"resourceVersion", osu.ResourceVersion,
		)

		if err := osupgradeController.HandleOSUpgrade(ctx, clients, namespace, nodeName, osu); err != nil {
			klog.ErrorS(err, "failed to handle osupgrade",
				"name", osu.Name,
				"node", nodeName,
			)
			continue
		}
	}

	return nil
}

func decodeOSUpgrade(item *unstructured.Unstructured) (*monov1alpha1.OSUpgrade, error) {
	var osu monov1alpha1.OSUpgrade
	if err := runtimeDefaultUnstructuredConverter.FromUnstructured(item.Object, &osu); err != nil {
		return nil, fmt.Errorf("convert unstructured to OSUpgrade: %w", err)
	}
	return &osu, nil
}

func matchesNode(osu *monov1alpha1.OSUpgrade, nodeName string, nodeLabels labels.Set) bool {
	if osu == nil {
		return false
	}

	sel := osu.Spec.NodeSelector
	if sel == nil {
		// No selector means "match all nodes".
		return true
	}

	selector, err := metav1.LabelSelectorAsSelector(sel)
	if err != nil {
		klog.ErrorS(err, "invalid node selector on osupgrade", "name", osu.Name)
		return false
	}

	if selector.Empty() {
		return true
	}

	if selector.Matches(nodeLabels) {
		return true
	}

	return false
}

func statusPhase(st *monov1alpha1.OSUpgradeStatus) string {
	if st == nil {
		return ""
	}
	return string(st.Phase)
}